Hexa-hydrocarbylphosphoramide solvents for halogenated aromatic insecticides



Un t s P en HEXA HYDROCARBYLPHOSPHORAMIDE SOL- VENTS FOR HALOGENATED AROMATIC IN- SECTICIDES Samuel C. Camp, Gibsonia, and Donald R. Stevens,

Wilkinsburg, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Application January 13, 1956 Serial No. 558,827

Claims. (Cl. 167-42) spray. Other halogen-containing aromatic insecticide toxicants can be applied in like manner.

A problem frequently encountered in the preparation of,insecticidal sprays is the choice of a proper solvent.

The choice is dependent on factors such as evaporating properties, solvent power, chemical activity, fiash point, odor, availability and cost. Petroleum hydrocarbon fractions meet most of the desired requirements and, asa consequence, have been used extensively as solvents and liquid carriers for various insecticide toxicants. The halogen-containing aromatic insecticides are representative of compounds that have been applied in liquid petroleum hydrocarbon compositions.

The physical and chemical properties of the petroleum hydrocarbon carriers will vary with the type of insecticidal composition desired. For example, the lighter petroleum fractions boiling within the naphtha range are ordinarily used for household sprays, while heavier fractions such as the paraffinic lubricating distillates can be used for agricultural sprays and the like. It should be understood that a wide variety of these hydrocarbon fractions are suitable as liquid carriers for halogen-containing aromatic insecticides.

Although relatively paraflinic petroleum hydrocarbon fractions boiling within the naphtha range have been most desirable as liquid carriers for insecticide toxicants, they are, as a general rule, poor solvents for the halogencontaining aromatic insecticides. Such fractions are ordinarily rich in aliphatic hydrocarbons, which are believed to be responsible for the poor solubility. To illustrate generally, moth and :bed bug sprays require about five percent by weight of DDT in solution. The solubility of DDT in naphtha at 26 C. is about 6.21 grams per 100 ml. of solution. At 3.3 C. it is about 3.8 grams and at 18 C. (about 0 F.) it is approximately 3 grams. Thus a naphtha solution of DDT prepared at room temperature will contain in solution about 6 grams of the insecticide per 100 ml. of solution but will precipitate out about 3 grams upon cooling to -l8 C. The precipitation of the toxic ingredient from solution is undesirable because it diminishes the killing power of the composition and because the precipitated toxicant does not easily redissolve even upon heating; accordingly such solutions'cannot bestored in cold weather.

.To increase the solubility of the halogenated aromatic insecticides it has become the general practice to use accessory solvents or solutizers in addition to the liquid carrier. Thus in formulations, usedcommercially, eertain aromatic hydrocarbon accessory solvents forhalogenated aromatic insecticides, particularly the alkylated naphthalenes or petroleum fractions predominating in them, have been employed; these petroleum fractions ordinarily contain from 30 to percent or more aromatic hydrocarbons. See US. Patent 2,448,665. To demonstrate, a household insecticidal spray used commercially containing 5 grams of DDT per ml. of solution has been prepared by blending 83.3 parts by volume of a deodorized petroleum spray naphtha and 13.2 parts by volume of a petroleum fraction containing 82 percent of aromatic hydrocarbons such as the alkyl naphthalenes. The naphtha is a straight run deodorized, colorless fraction generally characterized by being rich in aliphatic hydrocarbons of relatively low molecular weight. It is prepared by treating a straight run petro leum distillate with sulfuric acid to remove foreign colors and odors. Typical properties of the fraction are an initial boiling point of 366 F., a 50 percent point of 418 R, an end point of 484 F., a flash point of 154 F. and a representative specific gravity of about 0.768. A

typical aromatic hydrocarbon accessory solvent is obtained by a selective solvent treatment of a high boiling cut from a catalytically cracked petroleum distillate. The fraction used was characterized by an initial boiling point of 337 F., a 50 percent point of 442 R, an end point of 630 F., a flash point of F., and it contains about 82 percent aromatic hydrocarbons generally identified as alkyl naphthalenes. (These two fractions, that is, the deodorized naphtha fraction and the aromatic hydrocarbon fraction, will be referred to hereinafter in the de-' tailed description of the invention.) To obtain a final insecticide solution stable at about --18 C. (0 F.) and containing 5 grams of DDT per 100 ml. of solution, a concentrate is prepared by dissolving 30 grams of DDT per 100 ml. of the aromatic hydrocarbon solvent and then blending 16.7 parts by volume of this concentrate with 83.3 parts by volume of the petroleum naphtha.

Although the employment of the above described aromatic hydrocarbon accessory solvent has solved to some extent the problem of the solubility of the halogenated aromatic insecticides in the usual petroleum hydrocarbon solvents, the use of such fractions in insecticidal compositions is objectionable because of their disagreeable moth-ball odor. Objects sprayed with insecticidal solutions containing such accessory solvent retain the odor for long periods of time. This, of course, is objectionable in household insecticidal sprays. A further objection to the use of this accessory'solvent is that it causes foliage damage such as burning when applied to plants as in agricultural sprays.

We have now discovered that we can prepare improved substantially odorless insecticidal compositions comprising a halogenated aromatic insecticide toxicant and a relatively parafiinic petroleum hydrocarbon solvent as a carrier therefor by employing as the accessory solvent a normally liquid hexa-hydrocarbylphosphoramide. Mix- [2,2-bis(parachlorophenyl). 1,1-dichloroethane], Moth Patented Mar. 31, 1958 oxychlor [2,2-bis(paramethoxyphenyl)-1,1,1-trichloroethane], bis(parachlorophenoxy)methane, pentachlorophenol (C Cl OH), lindane (gamma isomer of benzene hexachloride, i.e., C H Cl and the like. All of such compounds present the problem of limited solubility in the petroleum hydrocarbon solvents rich in paratfins which are so generally used as carriers in liquid insecticidal compositions.

The liquid hexa-hydrocarbylphosphoramides and their mixtures possess unexpected solvent properties for the halogen-containing aromatic insecticide toxicants, and their solutizing or accessory solvency properties enable the solution of large quantities of these toxicants in relatively paraffinic petroleum hydrocarbon solvents used as. carriers, as will be shown hereinafter. Examples of the hexa-hydrocarbylphosphoramide solvents of our invention are hexamethylphosphoramide, hexaethylphosphoramide, hexapropylphosphoramide, hexaisopropylphosphorarnide, hexa-n-butylphosphoramide, hexa-secbutylphosphoramide, hexa-t-butylphosphoramide, hexaamylphosphoramide, hexa-hexylphosphoramide, hexa-Z- ethylhexylphosphoramide, hexaphenylphosphoramide, and the like. As will be noted, the hydrocarbyl radical is an alkyl or aryl radical composed of carbon and hydrogen.

In general, the liquid amide solvents of our invention can be used in combination with any of the relatively paraflinic petroleum hydrocarbon solvents used as carriers. To illustrate, in household and residual sprays there can be employed the petroleum hydrocarbon fractions having an ASTM distillation range of from 300 to 700 F. Kerosenes having ASTM distillation ranges of from about 350 to 510 F. and a fiash point of at least 130 F. are preferred. We have heretofore described a deodorized petroleum naphtha used commereially, having an ASTM distillation range of from about 366 F. to 484 F. and a flash point of 154 F. For agricultural sprays, heavier petroleum hydrocarbon fractions such as paraflinic lubricating distillates can be used.

In one aspect of our invention We have prepared insecticidal compositions comprising a liquid carrier such as a deodorized petroleum naphtha, a liquid amide solvent selected from the hexa-hydrocarbylphosphoramides and mixtures thereof, and a halogenated aromatic insecticide toxicant.

In another aspect of our invention we have prepared insecticidal compositions comprising a liquid carrier such as a deodorized petroleum naphtha, and a blend of an aromatic hydrocarbon accessory solvent for halogenated aromatic insecticides and a normally liquid amide selected from the hexa-hydrocarbylphosphoramides and mixtures thereof, and a halogenated aromatic insecticide toxicant.

Regardless of whether a liquid amide solvent or a blend of a liquid amide solvent and an aromatic hydrocarbon solvent is employed as the solutizer or accessory solvent, a sutficient amount of the normally liquid amide solvent is used in the composition to dissolve the desired amount of insecticide toxicant and to obtain a substantially odorless product.

It is not possible to specify exactly the amounts of liquid amide solvent to be employed in every instance since the amount to be used will vary with the concentration of the insecticide toxicant desired in the final composition, with the specific accessory solvent employed and With the solubility of the toxicant in the liquid carrier and in the accessory solvent or solvents employed. In general, however, we can prepare insecticidal compositions containing from about 5 percent to 20 percent by weight of halogenated aromatic insecticide with from as little as 2 to as high as 12 percent by volume of the amide solvents while realizing the ad vantages of our invention. Since the solubility of a particular halogenated aromatic insecticide toxicant in a particular liquid amide solvent .canbe routinely determined, and since the odor characteristics can .also be routinely determined when using as part of the accessory solvent an aromatic hydrocarbon solvent, the volume of amide solvent to be employed in each particular instance can be simply ascertained by one skilled in the art.

As we have indicated earlier, insecticidal compositions in accordance with the invention can be prepared with a blend of an odorous aromatic hydrocarbon accessory solvent and a liquid amide accessory solvent to obtain substantially odorless compositions. We have found that the amide solvents of our invention can be used advantageously to supplant portions of the aromatic hydrocarbon solvent, thereby substantially eliminating the disadvantages attendant on using the aromatic hydrocarbon solvents while retaining its cost advantage. While the volume of aromatic hydrocarbon solvent to be supplanted by the liquid amide will vary with each particular insecticidal composition, in general, for household sprays substantially odorless commercial formulations can be prepared wherein the amount of aromatic hydrocarbon solvent is kept at a minimum level.

Although we have generally described the liquid amides as accessory solvents for household sprays, among others, we would ordinarily not employ the hexa-hydrocarbylphosphoramides in such formulations because of their high boiling points, although such use is not precluded. Their use as accessory solvents would be particularly appropriate in those applications where it is desired to maintain a liquid film containing the insecticide toxicant over an extended period of time.

The efiectiveness of the amide solutizers of our invention is further illustrated by the following specific examples.

In the examples, the solvent properties of blends of solvents and of the individual solvents for the various halogenated aromatic insecticides were determined by dissolving incremental amounts of insecticide at 26-28 C. and at --3.3 C. In each case a known volume of solvent or solvent blend was saturated with the toxic ingredient and the excess undissolved portion was separated, weighed and the amount dissolved determined.

Table I below shows the grams of DDT dissolved per' m1. of solution of hexamethylphosphoramide, a deodorized spray naphtha and the alkylnaphthalenecontaining aromatic petroleum accessory solvent described previously.

Table I Gr. DDI Gr. DDT Ex. No. Solvent Dissolved Dissolved at 26 C. at 3.3 C.

Naphtha G. 21 3. 83 Aromatic Petroleum Solvent.--" 38.2 28. 25 Hexamethylphosphoramide- 76.81

The solvent power of hexamethylphosphoramide for DDT is seen to be twice that of the aromatic petroleum solvent. 7

While we have demonstrated the advantageous solvent properties of the solutizers of our invention with DDT, they can also be used with excellent results with the other halogenated aromatic insecticide toxicants.

From the foregoing description and data it is apparent that numerous insecticidal compositions containing halogenated aromatic insecticide toxicants can be readily prepared to meet a variety of requirements. Thus, stable insecticidal compositions can be prepared by supplanting all or only part of the accessory aromatic petroleum solvent with the liquid amides of our invention. The resulting formulations possess improved properties such as cleaner evaporation, stability at low temperatures and substantially no odor. Moreover, our solvents and solvent blends do not appreciably lower the flash point of the naphtha base to which they are added. t

Commercial insecticidal compositions, such as household sprays containing from 2 to 5 percent of DDT or other halogen-containing aromatic insecticide toxicant, can be readily prepared by using a small amount of a liquid amide or a blend of liquid amide and aromatic petroleum solvent with a liquid carrier such as a deodorized petroleum fraction. Stable compositions of the halogen-containing aromatic insecticide toxicants can be prepared with from 5 percent or less by volume of the liquid amides or blends of liquid amides and aromatic petroleum solvent and 95 percent or more of a deodorized petroleum naphtha. Other insecticidal compositions, for example, in residual sprays or agricultural sprays where it is desired to maintain a thin film of the composition for prolonged periods of time, can also be prepared with the higher boiling point amide accessory solvents. For these latter formulations, the hexa-hydrocarbylphosphoramides of our invention are particularly well adapted.

In addition to the above compositions, it should also be understood that a halogen-containing insecticide toxicant, for example, DDT, can be conveniently prepared in concentrated solutions of the liquid amides of our invention, or blends of the liquid amide and aromatic petroleum solvent, and transported or stored as such. The concentrates are conveniently employed in preparing the final insecticide compositions by simple dilution thereof with the required amount of the carrier petroleum hydrocarbon solvent. Generally speaking, suitable concentrates will contain in excess of 20 grams, say from 30 to 70 grams, of halogen-containing aromatic insecticide toxicant per 100 ml. of solution in the liquid amides of the invention. These concentrates can also contain emulsifying agents such as the oil-soluble sulfonic acid soaps for emulsion spray formulations.

The insecticidal compositions of our invention are effective in the control of insects for which the halogenated aromatic insecticide toxicants are normally used. In addition they are stable at low temperatures, are substantially free from disagreeable odors and possess clean evaporating properties.

From the foregoing, it will be understood that many modifications will be apparent to those skilled in the art and resort may be had to such modifications and variations as fall within the spirit of the invention and scope of the appended claims.

We claim:

1. A substantially odorless insecticidal composition having improved solubility and residual toxicity characteristics comprising a halogenated aromatic insecticide 5 McCauley:

toxicant, a petroleum hydrocarbon solvent as a carrier therefor and as an accessory solvent a normally liquid hexa-hydrocarbylphosphoramide.

2. The composition of claim 1 wherein the accessory solvent is hexa-methylphosphorarnide.

3. The composition of claim 1 wherein the halogenated aromatic insecticide is 2,2-bis(parachlorophenyl)-l,l,ltrichloroethane.

I 4. The composition of claim 1 wherein the accessory solvent is present in an amount of from 2 to 12 percent by volume of the composition.

5. A substantially odorless insecticidal composition having improved solubility and residual toxicity charac- .teristics comprising a halogenated aromatic insecticide toxicant, a petroleum hydrocarbon solvent as a carrier therefor and an accessorysolvent consisting of a blend of an aromatic hydrocarbon solvent rich in alkylated 1 naphthalene and a normally liquid hexa-hydrocarbylphoramide.

10. A concentrate useful in the preparation of insec ticidal compositions comprising a halogenated aromatic insecticide toxicant dissolved in a blend of an aromatic hydrocarbon solvent rich in alkylated naphthalene and a liquid hexa-hydrocarbylphosphoramide solvent.

References Cited in the file of this patent FOREIGN PATENTS Great Britain May 14, 1928 OTHER REFERENCES US. Dept. of Agri., Bur. of But. and Plant Quarm, publ. No. E-742, February 1948, pp. 6 and 7.

I ones: Soap and Sanitary Chem. (November 1945), pp. -115 and 155.

Pests (April 1946),p. 5. 

1. A SUBSTANTIALLY ODORLESS INSECTICIDAL COMPOSITION HAVING IMPROVED SOLUBILITY AND RESIDUAL TOXICITY CHARACTERISTICS COMPRISING A HALOGENATED AROMATIC INSECTICIDE TOXICANT, A PETROLEUM HYDROCARBON SOLVENT AS A CARRIER THEREFOR AND AS AN ACCESSORY SOLVENT A NORMALLY LIQUID HEXA-HYDROCARBYLPHSPHORAMIDE. 